1. Field of the Invention
The invention relates to a thin film transistor (TFT) and a fabricating method thereof. More particularly, the invention relates to a TFT having an oxide semiconductor channel layer and a fabricating method of the TFT.
2. Description of Related Art
With the rising awareness of environmental protection, flat display panels featuring low power consumption, optimal space utilization, and high definition have gradually become the mainstream products in the market of the displays. Common flat display panels include liquid crystal displays, plasma displays, organic light emitting diode displays, and so forth. The most popular liquid crystal display exemplified herein is mainly comprised of a TFT array substrate, a color filter substrate, and a liquid crystal layer sandwiched between the two substrates. In the conventional TFT array substrate, an amorphous silicon (a-Si) TFT or a low-temperature polysilicon (LTPS) TFT often serves as a switch element of each sub-pixel. According to recent researches, the oxide semiconductor TFT has greater mobility than the a-Si TFT. The oxide semiconductor TFT has a more stable threshold voltage Vth than the LTPS TFT. Hence, the oxide semiconductor TFT has great potential for becoming the key element of the next-generation flat display panel.
In the conventional oxide semiconductor TFT, the threshold voltage Vth of the oxide semiconductor channel layer is shifted after the oxide semiconductor channel layer is irradiated by ultraviolet (UV) light or operated under negative bias stress, and thereby electric properties and reliability of the oxide semiconductor TFT are affected. As a result, how to resolve the issue of threshold voltage shifts in the oxide semiconductor TFT demands immediate attention of manufacturers.